mfd: Add companion chip in 88pm80x

in hw design, 800 is mainly for pmic control, while 805 for audio.
but there are 3 registers which controls class D speaker property,
and they are defined in 800 i2c client domain. so 805 codec driver
needs to use 800 i2c client to access class D speaker reg for
audio path management. so add this workaround for the purpose to
let 805 access 800 i2c in some scenario.

Signed-off-by: Qiao Zhou <[e-mail]>
Reviewed-by: Arnd Bergmann <[e-mail]>
Signed-off-by: Samuel Ortiz <[e-mail]>

drivers/mfd/88pm80x.c

···
 #include <linux/uaccess.h>
 #include <linux/err.h>
 
+/*
+ * workaround: some registers needed by pm805 are defined in pm800, so
+ * need to use this global variable to maintain the relation between
+ * pm800 and pm805. would remove it after HW chip fixes the issue.
+ */
+static struct pm80x_chip *g_pm80x_chip;
 
 const struct regmap_config pm80x_regmap_config = {
 	.reg_bits = 8,
···
 
 	device_init_wakeup(&client->dev, 1);
 
+	/*
+	 * workaround: set g_pm80x_chip to the first probed chip. if the
+	 * second chip is probed, just point to the companion to each
+	 * other so that pm805 can access those specific register. would
+	 * remove it after HW chip fixes the issue.
+	 */
+	if (!g_pm80x_chip)
+		g_pm80x_chip = chip;
+	else {
+		chip->companion = g_pm80x_chip->client;
+		g_pm80x_chip->companion = chip->client;
+	}
+
 	return 0;
 
 err_chip_id:
···
 int __devexit pm80x_deinit(struct i2c_client *client)
 {
 	struct pm80x_chip *chip = i2c_get_clientdata(client);
+
+	/*
+	 * workaround: clear the dependency between pm800 and pm805.
+	 * would remove it after HW chip fixes the issue.
+	 */
+	if (g_pm80x_chip->companion)
+		g_pm80x_chip->companion = NULL;
+	else
+		g_pm80x_chip = NULL;
 
 	regmap_exit(chip->regmap);
 	devm_kfree(&client->dev, chip);

include/linux/mfd/88pm80x.h

···
 	struct pm80x_subchip *subchip;
 	struct device *dev;
 	struct i2c_client *client;
+	struct i2c_client *companion;
 	struct regmap *regmap;
 	struct regmap_irq_chip *regmap_irq_chip;
 	struct regmap_irq_chip_data *irq_data;